Changing of The Guard
by Omoni
Summary: Another semi-fluffy fic. This fandom is in serious need of fluff. So this one is all about how Undyne spent a week trying to kick Asgore to the floor – and what happens when he offers her training. There is some mature language, but it's Undyne, so what did you expect? There are also not a lot of spoilers in this one, but still play the game anyway, got it?
_Writer's Note: This is probably going to be my last Undertale fanfic for a while, not because I've lost my writing bug, but because I've yet to come up with another idea (as all of the recent fics have been ideas lined up; this is last on this list). Again, this is based on in-game hints and speculation in which I fill in the gaps (and usually shoot myself in the foot as a result, but again, my entire fault and no one else's.), so if it's wrong, be nice when you tell me how much I suck. :3_

 **Changing of the Guard**

It was always like hitting a big, furry wall, but it still left her stunned. Undyne fell hard onto the ground beneath her, not quite used to being the one who fell, despite this being the tenth time. Behind her, being absolutely no help at all, she heard both Aaron and Shyren snicker, and she scowled angrily, her teeth bared. Quickly, hoping to silence their laughter, she picked up her iron spear and lunged again.

King Asgore didn't even pause in his pace, or look her way. He merely held up an enormous hand and grabbed the spearhead. Undyne felt the force of the impact rattle through her, and for a moment, her arms went numb, the spear dropping from her hands. The King also dropped it as well, continuing on his way, a bucket of snails under his other arm, holding the gigantic thing quite easily.

Undyne was panting, now, her face burning with humiliation and rage. Forgetting her spear, now, she lunged again, snarling out her frustration as she did do, instead hoping hand-to-hand combat would be his one weakness.

It wasn't. If anything, King Asgore seemed to find her enraged attack amusing, finally stopping in his stroll to fend off her flurry of kicks and punches – again with only one hand. When she misjudged the timing of one of her punches, Asgore's hand neatly slipped between her defences and landed a flat-palmed blow onto her stomach. She instantly lost her breath and went down again, for a moment blacking out, though the hit wasn't as hard as she was sure he was capable of.

This had been going on for exactly five days, two attacks a day, now. Undyne would stalk her prey in the most obscure of places, and whenever she'd figured she'd finally had him where she wanted – like now – she would always end up landing on her ass. Each and every time.

It had first begun as a kind of dare, as she was well-known for attacking and trying to best several people she encountered whenever she had the chance. At the time, she was fifteen – close to sixteen – and her two best friends, Aaron and Shyren, had refused to spar with her anymore, even Aaron. In fact, it was Aaron who dared her to try on the King, as he was probably the only one that would match her muscles (he winked when he said this while looking sadly at his already large pecs).

At first, she had laughter at the very idea. After all, everyone knew that King Asgore was a giant softie, and would hesitate to swat even a fly. Undyne figured, with her own special brand of confidence (at this point she had already "lost" her eye), that it wouldn't be a fair fight at all, because of course she would win.

Right?

Her gym and martial arts teachers had pretty much concluded teaching her either physical course, stating that they valued their own lives than continuing to teach her. This only added to her inflated confidence, so when she was dared by Aaron, she had to accept.

The first time, she, Aaron, and Shyren had first tried to ambush Asgore in the supermarket, Aaron stating that: "He'll be so distracted by food, he'll never see you coming ;)!" Up to that challenge, she had done just that, and had snuck up behind the King, to either tackle him or put him in a headlock.

That was the first time she discovered his brick wall of a back. She crashed backwards into one of the displays, earning her a week's unpaid work there for her troubles. He hadn't even noticed at first, until she crashed – and then he had turned to her in concern and _tried to help her up!_

From there, for Undyne, it was war. Her pride was hurt, her back was hurt, and her friends were reconsidering her value as their bodyguard (though not as their friend). Starting that very night, she knew – she _had_ to beat King Asgore.

This time marked the tenth time she had attacked him – and again, the same amount of losses. But on this day, she fully lost any hold on her temper, and all she could now see was bright, enraged red.

She dragged herself to her feet, still wheezing from the hit to her stomach, before she lunged again. She heard Aaron murmur, "That's _not_ good ;)!" to Shyren, but Undyne was beyond caring. With a scream, she crashed into the King of all Monsters and actually tried to both scratch and bite him in an attempt to take him down.

Asgore paused again, still holding his bucket, in bemusement, now, as the fiery fish-girl literally tried to defeat him tooth-and-claw. Carefully, with Undyne still attached, he set the bucket down and very easily extracted her from his back, holding her up and away from him, keeping her exactly arms-length. Furious, she kicked and punched at him, her face bright red and her eye black with both panic and rage.

He held her like that for what seemed like forever, until she finally exhausted herself and started trying to squirm out of his iron grip. Very carefully, he set her back down on the ground, and she stood, hunched over, gasping for breath, her eye still black and her face a snarl of hatred and humiliation.

Carefully, his eyes still on her, Asgore leaned down and picked up his bucket, noticing that Undyne watched his every move. Something clicked in his mind, then, and he suddenly saw, standing before him, an opportunity. While he had seen her previous nine attacks as amusing – even sometimes challenging, forcing him to remember his old warrior ways – it was this tenth time that he saw something different.

 _Determination._

"Excuse me," he said gently. Undyne glared at her, her black eye boring into his. "But… would you like to know how to beat me?"

From their hiding places, Shyren and Aaron exchanged looks. Shyren whispered, "Did he just say that?" in her musical voice, and when Aaron nodded and winked, she whistled a few more notes in her surprise, oddly making him feel a little sleepy.

Undyne gasped for breath, then shouted, as loudly as she could, _"What the hell do you think I've been trying to do?!"_

Instead of wincing at her sharp tone like everyone else did, the King merely smiled. "Failing at it."

Undyne's eye narrowed to a deadly slit, and she lunged at him again. But he merely held out his hand and placed it on her shoulder, halting her. His touch was firm, yes, but almost with a degree of gentleness, and she stopped, her hands up and clawed, still. When she looked up at him, however, her eye was slowly easing back to its normal yellow.

"I can teach you how," Asgore continued, squeezing her shoulder kindly, smiling wider. "I do always need promising young warriors for my Royal Guard."

Undyne stared at him, shock flooding her body so fast she felt shaky. "But… I want to _kick_ your ass, not _protect_ it!"

Asgore laughed, the sound so rich, genuine and warm, that Undyne was suddenly calmer. "What better way to learn than by the owner of said rear?" he added, breathless from laughter.

Undyne blinked at him slowly, before feeling a smile of her own spread from ear-to-ear, the gesture almost feral in form. "You're on."

* * *

"Aack—!"

Undyne wheezed this out with it ending in a squeak, her vision going dark as she slammed onto the ground beneath her. The fall was softened by practise mats, true, but the force of the hit was still hard enough to send her reeling. Instantly, the blue spear she had been holding vanished, as everything went black.

"Up you go, please," said Asgore calmly, bringing her back. Her vision still danced with black spots, but she obliged, making her way slowly, aware of how badly her whole body was aching.

She was now a full month into training with Asgore, and she both loved and loathed it. With his help, she had enrolled in advanced magical combat classes, and found herself far more comfortable wielding magical spears that her usual metal ones. The problem was that if her concentration shattered, so did her weapon – a problem she wouldn't master until many years later.

Falling on her ass was definitely a concentration-breaker. One, by now, she knew quite well.

Back on her feet, she wobbled a bit, desperately thirsty and covered in sweat, having been at this with Asgore for over an hour, though you'd never know it by looking at the King: he stood calmly, not a drop of sweat on him, holding his trident rather loosely as he waited for her to regain her composure.

"W-water?" she gasped out without thinking, her hands limp at her sides.

Asgore narrowed his eyes at her, and instantly she regretted her mistake. Before she could even try to parry it, he swung his trident and swept her feet out from under her once more.

She lay there, panting for breath, eyes shut, as he spoke to her, in a voice soft but still stern, the voice he used when he needed her to listen, and closely.

"When you're fighting for your life, do you expect your opponent to give you water, Undyne? If you fall down from thirst, do you expect your opponent to patiently give you the water you need to recover, before attacking again?"

"N-no, King Asgore," she rasped out, slowly pushing herself back onto her hands and knees.

"Right. What do you expect, then?"

She looked up at him, her hair loose and sticking to her sweaty face like seaweed. He looked back at her, his face carefully blank.

"T-to die," she answered honestly, lowering her gaze from his. "Without…" She lowered her head. "Without mercy."

Silence. Then, she felt his hand on her shoulder. She raised her head and found him kneeling in front of her, holding a glass of water in his other hand.

"Exactly," he agreed. There was a flicker in his eyes, then, something dark and sad that made her throat close up and her eyes burn. "Now drink this, and we'll start again."

* * *

 _"Fuh—uck!"_

Again, on her ass. Again, the loss of breath.

Suddenly, a trident slammed right over her neck, the tines barely affording her space to breath, barely wide enough for said neck. She froze, her eye wide and slowly blackening in fear.

This was new.

 _"Undyne,"_ snapped Asgore, staring down at her with a stern and furious face. "What. Did I tell you. About using. _That word?!"_

She stared at him, not even risking a swallow.

He stared at her, long and hard, before he pulled it away, and Undyne lay there, now gasping for breath, unwilling to admit just how close she had come to fainting.

It was month three, now, and her 16th birthday had gone by with very little comment or fanfare (though Asgore gave her a fish-shaped mug that she adored.). With it, she'd decided that it was time to upgrade her curse words.

Both Aaron and Shyren found it hilarious – especially Shyren, who was far too shy to swear. Their teachers, however, did not, and she ended up staying after school doing menial chores as a result more often than she'd ever admit. That, she could live with, as the tasks she was given were usually heavy lifting, which was a bonus work-out for her.

Asgore, however, was appalled in the verbal change in his student. The first time she said 'shit', he refused to teach her for the rest of the day. The following day, he'd overheard her say 'fuck it' on the phone – and found herself on her ass, phone clattering across the floor like a kid on ice.

"Say that word again," Asgore said tersely, "and you will absolutely regret it. If you want to be a Guard, you have to abide by my standards, and that includes your language." He paused, and he narrowed his eyes at her. "If I ever hear that word again, you will learn why I am still King."

With a gulp of fear, she had nodded, fully intending to keep her word and never use it in front of him again.

However, this time, it had just burst out, with both anger and pain, because was so sure – _so sure_ – that her new multi-spear technique would have broken his defences at last.

Instead, he merely deflected each spear with his usual blank expression. She was so shocked, she forgot to continue to attack, which was when he filled the space and floored her.

And now she was shaking from head to foot, covered in cold sweat and unable to move. Because in that attack, and in the look in his eyes when he had snapped at her…

She saw it. She was why they still called him King.

"I… I did tell you, Undyne," he was saying, sounding almost regretful. She didn't say a word, trying to calm herself, but it was too late – her eyes burned. She gritted her teeth, punching the ground beneath her, but no amount of floor abuse would cease the hot tears from spilling down her cheeks and into her ears and hair.

"Undyne?"

She swallowed, then growled out, "Yes, sir. You did tell me." To her dismay, her voice was choked.

"Oh, golly." Suddenly, he was kneeling beside her. "Undyne, I'm very sorry." When he tried to help her up, she jerked away, pushing herself up and averting her face from him, one hand holding herself up, the other hurriedly wiping her tears from her face. She kept her face away, yes, but still she trembled.

"Undyne—,"

 _"No,"_ she snarled, jerking away when he tried to touch her shoulder. "You _did_ tell me."

He was silent, and she took the time to calm down as best she could, slowing her breath and swallowing her tears. When she finally turned back to him, to her shame, _his_ eyes were now wet.

Shame, however, quickly turned to anger at seeing this. She didn't know why, but it did. She held her hands up above her head, and instantly her blue spears jolted to life above her, each one pointing right at him.

Something glinted in his eyes, then, something it took her hours later to recognise: Pride. Instantly, he was on his feet, as she drew herself first up to her knees, then back to her feet, her knees trembling but her spears bright and strong.

With a shout – the soon-to-be-infamous "Nnggaaaaaaah!" – she let the spears go. Again, Asgore deflected them, his once wet eyes now shining with that same pride. And her spears, this time, didn't stop, even when they were deflected, even when she was floored. She got back up and kept going.

She didn't best him that day, but something had changed between them. Undyne finally realised why Asgore was both loved and feared, and that, to him, the conduct of his guards was a reflection of that love and respect, and that included language as well as action.

"Hey," she said, towel around her neck, as Asgore moved to leave the training areas of the castle and back to New Home. "Wanna come over, have a drink together? I finally have two mugs." And she grinned at him.

He was surprised, but that changed quickly to delight. "That would be quite lovely, Undyne!"

"Then let's go!"

It was the very same night that she discovered marshmallows got stuck in his beard. And the same night she became friends with her teacher.

* * *

By the time she had learnt how to use four-directional spear-onslaught attacks, she had kept her language pristine and her determination blazing, now into her fifth month of training with him. When Asgore deflected them from each direction with his trident, still she kept going, using both trick red spears and multi-piled spears. Still he deflected.

She had expected all of that. For those past months, she had watched him deflect every single attack from every angle and speed without hesitating. But she had her own secret, one she had kept even from Aaron. ("I'm curious and suspicious of your growing muscles! Tell me the secret ;)!") And it was that secret that she had kept for this very moment, when it seemed even her top-tier attacks would fail.

When he deflected her final spear and stood ready for her next attack, she was ready. She summoned it, wearing a huge grin on her face.

Asgore eyed her, looking confused. He started towards her, as he usually did when he thought she wasn't attacking. She stood calm, her concentration behind him.

And suddenly, those golden spears jumped forward and caught him right off guard before him. With a shocked expression, he missed three of the six hits, and he landed, hard, on the ground.

Undyne's eye followed his fall, her smile suddenly falling from her face with him. As he was the one winded, suddenly her stomach clenched, and she stepped back, her smile gone, replaced by a small line of guilt.

She felt like _scum_.

Holding a hand to her roiling stomach, she started forward. "Asgore, I'm so… I'm so—,"

She froze in shock. He was lying there, yes. But he was chuckling, so hard his whole body shook, his eyes wet with tears of either his laughs… or that pride. Because he gasped out, "Whew! My goodness!" Then he looked right at her and…

…he was _beaming_ at her.

"Hoo, hoo," he laughed again, rubbing his head. "You _got_ , me, Undyne! That's _wonderful!"_

Undyne stared at him, still feeling sick. She didn't know why; the whole point _was_ to kick his ass, to learn how to beat him, wasn't it?

 _Was it?_

Wordlessly, she walked to his side and held both her hands out. With a smile, he took both into one of his, and she pulled him to his feet. Once there, she kept one hand on his shoulder, searching his gaze desperately, though for what, she didn't know.

He clapped a hand on her back, a gesture that several months ago would have made her stumble now merely made her stand up straighter. "That was an excellent… 'fake-out', is it called?" Undyne stared at Asgore as he laughed again, his crown off-kilter upon his head. "I didn't see it coming _at all_! Golly, Undyne, you're full of surprises! Did you teach that move to yourself?"

She nodded mutely. To her sudden embarrassment, she felt her eyes start to burn and she looked away, even as he added, "That's incredibly impressive, Undyne!" He paused, peering at her, and she averted her head away. "Aren't _you_ happy?"

 _"No,"_ she growled. "I feel like sh—like crap. I feel _terrible_."

"But, why? You've finally learnt how to beat me! It's exactly what we both wanted!"

Undyne's whole body twitched, her eye snaking over to him. "What are you talking about, 'what we both wanted'?" she demanded.

Asgore smiled. "My Royal Guard has gotten rather… lazy in their years without much action, and this doesn't encourage the younger ones to join up. I've been looking for a new Captain for too many years to count."

Undyne turned back to him, her face a perfect example of shock.

He nodded at her, continuing. "When the Hammer told me about you, how you kept trying to best everyone – even him! – I wondered about you. Like I said, not many kids nowadays really care about being warriors."

Undyne was still speechless, though her mouth was now open.

Asgore was still smiling at her so warmly she felt that hated burning again. "When you started attacking me, I was _thrilled!_ But I had to test your perseverance, first. And you proved me right. I do like being right."

Without control, she felt tears run down her cheeks. Gently, he placed his hand on her shoulder, looking at her with kindness. "I've never been so proud."

Undyne shut her eyes and gritted her teeth, clenching her fists at her sides. With a furious snarl, she crashed into him, hugging him harder than she had anyone else before. She was crying, now, crying the way she hated most: loud, messy and body-wrenching. She didn't know why, or even where from, the tears came, but she couldn't stop them, now. Not after what Asgore had just said.

Asgore, to her surprise, took her tears very well. He hugged her gently, taking her occasional punches to his shoulders and back quite calmly, one hand rubbing her back, the other atop her head. He did this so well, she suddenly remembered: Asgore was – had been – a father, so of course he knew how to comfort someone crying.

When she had exhausted herself, she hurriedly jerked away, using her shirt to dry her face. Asgore kept a hand on her back, and she sighed. "I suppose that's a deal-breaker?" she wondered, her voice as tired and drained as she felt. "A crybaby guard?"

"On the contrary," Asgore replied. "A perfect Captain of the Royal Guard."

She turned back to him. "You're serious, aren't you?"

"As a heart-attack." She made a face, and he laughed, before adding, "Yes, Undyne. I'm as serious as I can be."

Undyne looked up at him, and saw that his face was thrilled, yes, but also rather clear. "I'm gonna be Captain someday?" she asked.

"You _are_ Captain," he corrected. "As soon as you say yes."

Undyne paused, thinking. "Does that mean I get to train new soldiers, as well as drill the older ones?"

He nodded.

"I get to train the dumba-er- _dorks_ to fight?"

Asgore sighed, and did the unkingly act of rolling his eyes at that. "I suppose you could put it that way, if it makes you happy."

She grinned. Though some of the guilt still lingered, she knew she had earned the pride from her teacher. She gazed up at him and finally beamed back.

"You're on."

And so began the era – and terror – of Undyne, Captain of the Royal Guard.


End file.
